I didn't fully read all the posts so sorry if it was already mentioned but another source of engine vibration "all of a sudden" can be traced to the harmonic balancer. The inner and outer portions of the balancer are attached together by a thin piece of rubber. Its possible the outer piece (ring) slipped out of position causing an imbalance. The slippage would be impossible to see with the naked eye. The only way to check slippage is locate TDC on #1 piston using a stop or dial indicator through the spark plug hole and comparing the TDC mark on the balancer to the "0" on the timing chain cover. Good luck.